IMPORTANT DRUG-DRUG INTERACTIONS IN THE ELDERLY

Although drug-drug interactions constitute only a small proportion of adverse drug reactions, they are important because they are often pred ictable and therefore avoidable or manageable. Their frequency is rela ted to the age of the patient, the number of drugs prescribed, the num ber of physicians involved in the patient's care and the presence of i ncreasing frailty. The most important mechanisms for drug-drug interac tions are the inhibition or induction of drug metabolism, and pharmaco dynamic potentiation or antagonism. Interactions involving a loss of a ction of one of the drugs are at least as frequent as those involving an increased effect. It is likely that only about 10% of potential int eractions result in clinically significant events and, while death or serious clinical consequences are rare, low-grade, clinically unspecta cular morbidity in the elderly may be much more common. Nonspecific co mplaints (e.g. confusion, lethargy, weakness, dizziness, incontinence, depression, falling) should all prompt a closer look at the patient's drug list. There are a number of strategies that can be adopted to de crease the risk of potential clinical problems. The number of drugs pr escribed for each individual should be limited to as few as is necessa ry. The use of drugs should be reviewed regularly and unnecessary agen ts withdrawn if possible, with subsequent monitoring. Patients should be encouraged to engage in a 'prescribing partnership' by alerting phy sicians, pharmacists and other healthcare professionals to symptoms th at occur when new drugs are introduced. Physicians with a responsibili ty for elderly people in an institutional setting should develop a str ategy for monitoring their drug treatment. For those interactions that have come to clinical attention, it is important to review why they h appened and to plan for future prevention. Clinicians should also repo rt, via the appropriate postmarketing surveillance scheme, any drug-dr ug interactions they have encountered. Finally, multidisciplinary educ ation about the nature of physiological aging and its effect on drug h andling, and the possible presentations of drug-related disease in old er patients, is an important element in reducing interactions in the e lderly.